1. Field of the Invention
The present invention relates to a method of crystallizing an amorphous semiconductor thin film and a method of fabricating a poly-crystalline thin film transistor using the same, and more particularly, to a method of crystallizing an amorphous semiconductor thin film and a method of fabricating a poly-crystalline thin film transistor using the same, in which a protection film such as an oxide film is coated in advance before a metal induced lateral crystallization (MILC) heat treatment when an amorphous semiconductor thin film is crystallized using a MILC method, to thereby enabling the MILC heat treatment even in the air.
2. Description of the Related Art
In a method of forming a poly-crystalline silicon film which is used as a semiconductor layer of a thin film transistor, an amorphous silicon film is deposited on a substrate, and then processed at a predetermined temperature, to thus crystallize the amorphous silicon film into a poly-crystalline silicon film. Here, a metal induced lateral crystallization (MILC) method, a solid phase crystallization (SPC) method, and an eximer laser annealing (ELA) method are known as the amorphous silicon film crystallization method.
Among them, the MILC method does not only enable a batch processing using a conventional inexpensive heat treatment facility but also has many advantages of a relatively low processing temperature and a relatively short processing time.
A conventional method of fabricating a thin film transistor using a MILC method will follow with reference to FIGS. 1A through 1E.
FIGS. 1A through 1E are cross-sectional views for explaining a conventional thin film transistor fabrication method using a MILC technology, respectively.
Referring to FIG. 1A, an amorphous silicon film is deposited on an insulation substrate 10, and the amorphous silicon film is patterned using a semiconductor layer forming mask (not shown), to thereby form a semiconductor layer 11.
Referring to FIG. 1B, a gate oxide film and a gate electrode material are deposited on the substrate 10, and then sequentially patterned using a gate forming mask (not shown) to thereby form a gate electrode 13 and a gate insulation film 12.
Referring to FIG. 1C, a photosensitive film is formed on the whole surface of the substrate, and then a photosensitive film pattern 14 which is slightly larger than a gate pattern is formed using an off-set mask (not shown). Then, a crystallization induced metal film 15 for metal induced lateral crystallization (MILC) (hereinafter referred to as a “MILC metal film”) such as nickel (Ni) is deposited on the entire surface of the substrate.
Referring to FIG. 1D, the photosensitive film pattern 14 is removed by using a lift-off method, and thus the gate electrode 13 and the off-set portions 11a and 11b of the semiconductor layer 11 are exposed. Then, high-concentration impurities are ion-injected onto the substrate to thereby form a source region 11S and a drain region 11D.
Thereafter, referring to FIG. 1E, a MILC heat treatment is performed on the substrate at 400° C. through 600° C. under the inert gas, hydrogen, or vacuum atmosphere, to thereby crystallize the amorphous silicon film of the semiconductor layer 11 into a poly-crystalline silicon film. In this case, a portion contacting the metal film 15 is crystallized by a metal induced crystallization (MIC) method, and off-set portions which do not contact the metal film 15 and a channel region 11C below the gate insulation film 12 are crystallized by a metal induced lateral crystallization (MILC) method.
Referring to FIG. 1F, an interlayer insulation film 16 is deposited on the substrate 10. Then, contact holes 17 with respect to the gate electrode 13, the source region 11S and the drain region 11D are formed using a contact forming mask (not shown). Then, a metal-wiring metal film is deposited and then patterned using a metal-wiring forming mask (not shown) to thereby form a metal-wiring pattern 18.
As described above, a MILC heat treatment is performed at a state where amorphous silicon is exposed in the case of a conventional thin film transistor fabrication method using the MILC method. Therefore, the heat treatment is performed under an inert gas atmosphere such as nitrogen or argon, under a reducing gas atmosphere such as hydrogen, or under a vacuum atmosphere. Thus, tremendous expenses are required in order to maintain the above-described atmosphere. In particular, as size of the substrate becomes large, the maintenance cost for the atmosphere cannot but increase by geometric progression.